[volt-nuts] 3458A reference boards on ebay

Hendrik Dietrich don_hendi at gmx.de
Sat Jan 31 02:59:00 EST 2015


Am 31.01.2015 06:21, schrieb Joel Setton:
> I'll be happy to design a PCB, and have bare PCB prototypes made.
> Sourcing parts and purchasing them will be another, larger project!
>
> Joel Setton
>

Here's my design in eagle, the prototype is working fine but there is 
still room for improvement:

http://dg3hda.primeintrag.org/lib/exe/fetch.php?media=rev0-econi.zip

Free for volt-nut useage, of course.

I tried to remove some voodoo that you will be told if using the 
internet as source, but there are leftovers as I was afraid that they 
could have something:

There are some extra cuts close to the connectors ("stress relief") 
which are really unnecessary - after manufacture I became aware of a 
experiment reported on EEVBlog that strong bending with a vise gave no 
visible response of a LM399-based PCB on 6.5 digit DVMs.

A few drills around the LTZ itself which are cheaper to produce but 
might or might not have some benefit - kovar lead and soldering joint 
are thermally closer to the temperature controlled site, so less risk of 
_changing_ EMF voltages there.

The opamp at the output causes some tiny little degradation but gives a 
lot of protection in case of accidents and abuse.
This core circuit can be pushed around to make it much more compact, if 
somebody does it the regained space should be used to add some filtering 
against EMI.

The resistors are not Vishay but Rhopoint Econistors.  My LTZ1000A was 
sourced from ebay, and no dud.

Hendrik



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